Liquid crystal panels, which are thin and light, are widely used as the display screens of portable information terminals.
The liquid crystal panels include transmission type liquid crystal panels and reflection type liquid crystal panels.
FIG. 15A is a sectional view of the transmission type liquid crystal panel. As illustrated in FIG. 15A, a polarizer 214 is sandwiched between a glass substrate 210 and a glass substrate 212. On the glass substrate 212, bus lines 216, etc. are formed. A liquid crystal 220 is sealed between the glass substrate 212 and a glass substrate 218. Color filters 224a, 224b, 224c are sandwiched between the glass substrate 218 and the glass substrate 222. A polarizer 228 is sandwiched between the glass substrate 222 and the glass substrate 226.
FIG. 15B is a sectional view of the reflection type liquid crystal panel. As illustrated in FIG. 15B, in the reflection type liquid crystal panel, a mirror 230 is sandwiched between the glass substrate 210 and the glass substrate 212. The mirror 230 is for reflecting light entering at the upper surface of the reflection type liquid crystal panel.
The Liquid crystal itself is not luminous, and illumination is necessary to see the information displayed on the liquid crystal panels.
In the transmission type liquid crystal panel, a lighting apparatus is disposed on the side of the lower side of the liquid crystal panel.
In the reflection type liquid crystal panel, no lighting apparatus is essentially required when the display screen is watched in environments with sun light or room lights. However, a lighting apparatus is required so that the display screen can be watched in environments without illumination. The lighting apparatus is disposed on the side of the upper side of the liquid crystal panel.
FIG. 16 is a perspective view of the proposed lighting apparatus. As illustrated in FIG. 16, the proposed lighting apparatus 110 includes LEDs 112a, 112b which emit light, a linear light conductor 114 which converts the light from the LEDs 112a, 112b to linear light to emit the linear light, and a plane light conductor 116 which converts the liner light emitted by the liner light conductor 114 to plane light to emit the plane light. On the rear side of the linear light conductor 114, i.e., the reflection side, a plurality of light reflecting parts 120 are formed in stripes. A reflection coat film 118 is formed on the reflection side of the linear light conductor 114.
FIGS. 17A and 17B are a perspective view and a plan view of the linear light conductor of the proposed lighting apparatus. As illustrated in FIGS. 17A and 17B, the light emitted by the LEDs 112a, 112b is reflected on the rear side of the linear light conductor 114, i.e., the plane of the light reflection parts 120 formed on the reflection side to be emitted at the front side of the linear light conductor 114, e.g., the exit side. The linear light emitted at the exit side of the linear light conductor 114 is converted to plane light by the plane light conductor 116 to be emitted at the plane of the plane light conductor 116.
In this proposed lighting apparatus, the liquid crystal panel can be illuminated in plane. Such lighting apparatus is described in, e.g., the specification of Japanese Patent Application Unexamined Publication No. Hei 10-260405.
However, the proposed lighting apparatus described above cannot illuminate the liquid crystal panel with a uniform light intensity distribution, as will be described below.
FIG. 18 is a graph of an intensity distribution of light emitted by the linear light conductor of the proposed lighting apparatus. Positions from the center of the linear light conductor 114 are taken on the horizontal axis, and on the vertical axis, light intensities are taken.
As indicated in FIG. 18, in the proposed lighting apparatus, the intensity distribution of the light exiting from the linear light conductor 114 is not uniform and has parts of high intensities and parts of low intensities. An intensity distribution of the light emitted by the linear light conductor 114 is reflected in an intensity distribution of the light emitted by the planar light conductor 116. Accordingly, the intensity distribution of the light emitted by the planar light conductor 116 is not uniform and has parts of high light intensities and parts of low light intensities. Accordingly, the liquid crystal display using the proposed lighting apparatus cannot have good display characteristics.
An object of the present invention is to provide a lighting apparatus which can illuminate with a uniform light intensity, and a liquid crystal display using the lighting apparatus, which has good display characteristics.